Gas turbine shroud cooling

ABSTRACT

A shroud segment for a casing of gas turbine includes a body configured for attachment to the casing proximate a localized critical process location within the casing. The body has a leading edge, a trailing edge, and two side edges. The critical process location is located between the leading edge and the trailing edge when the body is attached to the casing. A cooling passage is defined in the body along one of the side edges with one of an inlet or an outlet proximate the critical process location. The cooling passage is configured large enough to cool the one side edge adjacent the cooling passage to a desired level during operation of the gas turbine. The critical process locations may be related to temperatures, pressures or other measurable features of the gas turbine environment when in use.

FIELD OF THE INVENTION

The present invention generally involves cooling a turbine shroudelement that may be located in a hot gas path of the turbine.

BACKGROUND OF THE INVENTION

Turbines are widely used in a variety of aviation, industrial, and powergeneration applications to perform work. Each turbine generally includesalternating stages of peripherally mounted stator vanes and rotatingblades. The stator vanes may be attached to a stationary component suchas a casing that surrounds the turbine, and the rotating blades may beattached to a rotor located along an axial centerline of the turbine. Acompressed working fluid, such as steam, combustion gases, or air, flowsalong a gas path through the turbine to produce work. The stator vanesaccelerate and direct the compressed working fluid onto the subsequentstage of rotating blades to impart motion to the rotating blades, thusturning the rotor and performing work. If any compressed working fluidmoves radially outside of the desired flow path, the efficiency of theturbine may be reduces. As a result, the casing surrounding the turbineoften includes a radially inner shell of shrouds, often formed insegments. The shrouds surround and define the outer perimeter of the hotgas path and may be located around both stator vanes and rotatingblades.

The turbine shrouds are typically cooled in some fashion to remove heattransferred by the hot gas path. U.S. Pat. No. 7,284,954 describes aturbine shroud segment that includes many small cooling fluid passagesmachined throughout the turbine shroud. A fluid such as compressed airfrom an upstream compressor may be supplied through the fluid passagesto cool the turbine shroud. Other shroud segments utilize a singlelarger “core” flow path cast in place rather than multiple smallmachined passages as above. The core extends along an entire side of theshroud segment from an axially upstream end to an axially downstreamend.

While both types of shroud segment cooling passages work well, continuedimprovements in systems to cool turbine shrouds would be welcome,particularly systems that improve the amount of cooling provided by agiven flow and/or that allow selective targeting of cooling at desiredlocations axially along the shroud segments.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention are set forth below in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

According to certain aspects of the present disclosure, a shroud segmentfor a casing of gas turbine may include a body configured for attachmentto the casing proximate a localized critical process location within thecasing. The body has a leading edge, a trailing edge, and two sideedges, as well as a first surface for facing the casing and a secondsurface opposite the first surface for facing a hot gas path. Thecritical process location is located between the leading edge and thetrailing edge when the body is attached to the casing. At least twocooling passages are defined in the body along one of the side edges. Afirst of the cooling passages has an inlet and extends to an outlet, oneof the inlet or outlet being adjacent the critical process location. Asecond of the cooling passages has an inlet and extends to an outlet,one of the inlet or the outlet being adjacent the critical processlocation. The first and second cooling passages are configured largeenough to cool the one side edge to a desired level during operation ofthe gas turbine. Various options and modifications are possible.

According to certain other aspects of the present disclosure, a gasturbine may include a compressor section, a combustion sectiondownstream from the compressor section, and a turbine section downstreamfrom the combustion section. The turbine section includes a casingdefining a localized critical process location and a plurality of shroudsegments circumferentially attached to the casing. Each shroud segmentincludes a body configured for attachment to the casing. At least one ofthe bodies has a leading edge, a trailing edge, and two side edges, aswell as a first surface facing the casing and a second surface oppositethe first surface facing a hot gas path. The critical process locationis located between the leading edge and the trailing edge when the bodyis attached to the casing. At least two cooling passages are defined inthe body along one of the side edges. A first of the cooling passageshas an inlet and extends to an outlet, one of the inlet or outlet beingadjacent the critical process location. A second of the cooling passageshas an inlet and extends to an outlet, one of the inlet or the outletbeing adjacent the critical process location. The first and secondcooling passages are configured large enough to cool the one side edgeto a desired level during operation of the gas turbine. As above,various options and modifications are possible.

Those of ordinary skill in the art will better appreciate the featuresand aspects of such embodiments, and others, upon review of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a schematic view of an exemplary gas turbine incorporatingaspects of the present disclosure;

FIG. 2 is a simplified cross-section view of a portion of the gasturbine of FIG. 1 showing a shroud segment;

FIG. 3 is a top view of a shroud segment as in FIG. 2;

FIG. 4 is a side view of the shroud segment of FIG. 3;

FIG. 5 is a sectional view of the shroud segment taken along line 5-5 inFIG. 3;

FIG. 6 is an isometric view of the shroud segment of FIG. 3;

FIG. 7 is a top view of a first alternate shroud segment;

FIG. 8 is a top view of a second alternate shroud segment; and

FIG. 9 is a top view of a third alternate shroud segment.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention. As used herein, theterms “first”, “second”, and “third” may be used interchangeably todistinguish one component from another and are not intended to signifylocation or importance of the individual components. In addition, theterms “upstream” and “downstream” refer to the relative location ofcomponents in a fluid pathway. For example, component A is upstream fromcomponent B if a fluid flows from component A to component B.Conversely, component B is downstream from component A if component Breceives a fluid flow from component A.

Each example is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that modifications and variations can be made in thepresent invention without departing from the scope or spirit thereof.For instance, features illustrated or described as part of oneembodiment may be used on another embodiment to yield a still furtherembodiment. Thus, it is intended that the present invention covers suchmodifications and variations as come within the scope of the appendedclaims and their equivalents.

FIG. 1 is a schematic view of an exemplary gas turbine that canincorporate a shroud element according to the present disclosure. Asillustrated, gas turbine 110 includes an inlet section 111, a compressorsection 112, a combustion section 114, a turbine section 116, and anexhaust section 117. A shaft (rotor) 122 may be common to compressorsection 112 and turbine section 116, and may further connect to agenerator 105 for generating electricity.

The compressor section 112 may include an axial flow compressor in whicha working fluid 100, such as ambient air, enters the compressor from theinlet section 111 and passes through alternating stages 113 ofstationary vanes and rotating blades (shown schematically in FIG. 1).Compressor casing 118 contains the working fluid 100 as the stationaryvanes and rotating blades accelerate and redirect the working fluid toproduce a continuous flow of compressed working fluid. The majority ofthe compressed working fluid flows downstream through the combustionsection 114 and then the turbine section 116.

The combustion section 114 may include any type of combustor known inthe art. A combustor casing 115 may circumferentially surround some orall of the combustion section 114 to direct the compressed working fluid100 from the compressor section 112 to a combustion chamber 119. Fuel101 is also supplied to the combustion chamber 119. Possible fuelsinclude, for example, one or more of blast furnace gas, coke oven gas,natural gas, vaporized liquefied natural gas (LNG), hydrogen, andpropane. The compressed working fluid 100 mixes with fuel 101 in thecombustion chamber 119 where it ignites to generate combustion gaseshaving a high temperature and pressure. The combustion gases then enterthe turbine section 116.

As shown in FIGS. 1 and 2, within turbine section 116, alternatingstages of rotating blades (buckets) 124 and stationary blades (nozzles)126 are attached to rotor 122 and turbine casing 120, respectively.Working fluid 100, such as steam, combustion gases, or air, flows alonga hot gas path through gas turbine 110 from left to right as shown inFIG. 2. The first stage of stationary nozzles 126 accelerates anddirects the working fluid 100 onto the first stage of rotating blades124, causing the first stage of rotating blades 124 and rotor 122 torotate. Working fluid 100 then flows across the second stage ofstationary nozzles 126 which accelerates and redirects the working fluidto the next stage of rotating blades (see FIG. 1), and the processrepeats for each subsequent stage.

As shown schematically in FIG. 1, the radially inward portion of turbinecasing 120 may include a series of shrouds 128. Shrouds 128 in FIG. 1are formed around blades 124. FIG. 2 shows shrouds 128 formed aroundboth blades 124 and nozzles 126. Shrouds 128 may be formed in segments,such as segment 130 of FIGS. 2-6. It should be understood that, althoughan example of a shroud segment related to a blade 124 is shown, thepresent disclosure incorporates shroud segments formed around nozzles124 as well. Therefore, no limitation as to location of shrouds withincasing 120 should be made.

As shown in FIG. 3, each shroud segment 130 may generally comprise abody having a plurality of sides. Specifically, each segment 130 has aleading edge 132, a trailing edge 134, and two side edges 136 and 138. Afirst surface 140 faces (radially outwardly) toward casing 120 and asecond surface 142 opposite the first surface faces (radially inwardly)toward the hot gas path where the working fluid 100 flows.

A critical process location (defined below) 144 is located betweenleading edge 132 and the trailing edge 134, generally in alignment withrotating blades 124. The critical process location 144 could be, forexample, a maximum or other critical temperature location along thesegment during gas turbine use, a maximum or other critical pressurelocation along the segment during gas turbine use, a maximum or othercritical gas side heat transfer coefficient location, or a maximum orother critical stress location. The critical process location 144 couldbe a location where cooling gases can enter or exit the segment aftertravelling through a passageway allowing for sufficient cooling of thesegment, while still respecting back flow margin limitations.

Also, the critical process location need not be an absolute maximum, itcould be any desired value that can be used to determine optimal flowand heat transfer characteristics within the gas turbine or within thesegment itself. Much depends on the desired characteristics of the gasturbine, flow at the location of segment 130, etc. The critical processlocation along segment 130 could vary at different stages within a gasturbine. Further, two or more of such critical process locations couldexist along a single segment 130.

At least two cooling passages 146,148 are defined in segment 130 alongone of side edges 136. First cooling passage 146 has an inlet 150 thatmay be (as shown) on first surface 140 near leading edge 132. Firstcooling passage 146 also has an outlet 152 adjacent critical processlocation 144. Second cooling passage 148 has an inlet 154 that may be(as shown) on first surface 140 adjacent critical process location 144.Second cooling passage 148 has at least one outlet 156 that may be (asshown) near trailing edge 134.

It should be understood that flow through either or both of passages146,148 could be reverse of that which is shown. For example, flow infirst passage 146 could be counter (directed upstream) to that throughsecond passage 148. In other words, flow could run from opening 152 toopening 150 (reversing inlet/outlet functions), if desired. Flow throughsecond passage 148 could also be similarly reversed.

First and second cooling passages 146,148 may be formed by castingrather than machining. For example, as is known a mold may be used inwhich a fill substance is provided matching the path of first and secondcooling passages 146,148, the fill substance being burned off and/orchemically removed afterward leaving the passages. Such manufactureusing casting of at least some portion of the passages may be more costeffective than machining the passages or multiple smaller passages. Evenif the passages are formed substantially by casting, inlets and outletsto the passages or other features may be machined as part of themanufacture.

First and second cooling passages 146,148 may be configured large enoughto cool side edge 136 and/or a related area to a desired level duringoperation of the gas turbine. The passage sizes are configured to allowsufficient flow that back flow margins are respected, and heat transferis sufficient to cool segment 130 to a desired temperature. If desired,in one example of a gas turbine, a segment 130 with a length of about6.5 inch, a width of about 3.0 inch, and general thickness of about 0.25inch, passages 146, 148 may be of a cross-section of about 0.025 squareinch. Accordingly, numerous small passages spread along the locations ofcooling passages 146,148 are not required to cool segment 130.

As shown, an additional set of cooling passages 158,160 can be providedon other side edge 138. Passages 158,160 may if desired but notnecessarily be substantially symmetrical to passages 146,148 along acentral axis running between leading edge 132 and trailing edge 134. Asabove first cooling passage 158 has an inlet 162 which may be (as shown)on first surface 140 near leading edge 132. First cooling passage 158also has an outlet 164 adjacent critical process location 144. Secondcooling passage 160 has an inlet 166 which may be (as shown) on firstsurface 140 adjacent critical process location 144. Second coolingpassage 160 has at least one outlet 168 which may be (as shown) neartrailing edge 134. As shown, inlet 150 and inlet 162 are a common,single inlet. However, as discussed below, the inlets 150,162 may beseparate.

Various options and modifications are possible. For example, as shown inFIG. 3, both second passages 148,160 may have multiple outlets 156,168,which may be along trailing edge 134. Such multiple exits may bemachined or cast, and may be employed to cool trailing edge 134 ifspaced sufficiently from second passages 148,160 to require additionalcooling. Some or all of such multiple outlets could instead or also exitsegment 130 at locations other than trailing edge 134 if desired.

Alternatively, as shown in FIG. 7, modified segment 130′ has firstpassages 146′,158′ each with their own individual inlets 150,162 withfirst portions 170,172 and second portions 174,176 leading to outlets152,164. As shown in FIG. 3, first portions 170,172 are in communicationwith each other; as shown. If desired, some or all of the inlets insegment 130 or 130′ could also be located elsewhere other than firstsurface 140.

As another alternative, as shown in FIG. 8, modified segment 130″ hassecond passages 148′,160′ each with individual inlets 154,166 leading tofirst portions 178,180 and second portions 182,184 and then outlet(s)156,168, as above. However, second portions 182,184 in FIG. 8 are incommunication with each other. Therefore, instead of the constructionshown in FIG. 3, having one first passage upstream of location 144 andtwo second passages downstream of location 144, a shroud segment couldbe made as shown in FIG. 8 with one upstream passage and one downstreampassage split along the side edges 136,138 at location 144.

Alternatively, as shown in FIG. 9, splits could be provided at two ormore critical process locations along the shroud segment. Along one sideof segment 130′″, a first passageway 146 extends from inlet 150 tooutlet 152, a second passageway 148′ extends from inlet 154 to outlet153 and a third passageway 179 extends from inlet 155 to outlets 156.Similarly, along the other side, a first passageway 158 extends frominlet 162 to outlet 164, a second passageway 160′ extends from inlet 166to outlet 165 and a third passageway 181 extends from inlet 167 tooutlets 168. Accordingly, FIG. 9 illustrates that more than one splitcan be made between leading edge 132 and trailing edge 134 at criticalprocess locations, as desired. It should also be understood that splitsneed not be symmetrical or even along a given side of the segments orbetween sides of the segments.

The segments above can be mounted to turbine casings in various knownways, via hooks, impingement plates, clips, etc. The present inventionis not limited to any such mounting arrangement, cooling mode, or anyparticular fluid used to cool the shroud segment. For example, suchmounting may or may not provide that the cooling fluid first impacts thesegments to provide impingement cooling to the bulk of the segmentbefore some fluid flows through the disclosed passageways. Also, thesegments may include mounting structures, cooling passage openings,etc., for receiving, contacting or cooling nozzles 126 if the segmentsare located along a row of nozzles as opposed to a row of blades 124.

It is anticipated that the various embodiments of the shroud segmentsshown above may be manufactured at lower costs than previous designs.Specifically, the segments may be cast or forged, with reduced machiningrequired for inlets and outlets and the larger passages being formed bycasting. In this manner, the shroud may be readily manufactured toinclude the desired fluid passages that provide cooling to the sides ofthe segments. By splitting the passages at critical process location(s)144 where maximum temperature, pressure or other measurable parameters(maximums or not), cooling can be beneficially located at a desiredpoint while providing a more efficient flow, with less leakage. Thesegments can thus be tuned in various ways to improve thermal and flowperformance.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A shroud segment for a casing of gas turbinecomprising: a body configured for attachment to the casing proximate alocalized critical process location within the casing, the body having aleading edge, a trailing edge, and two side edges, the body having afirst surface for facing the casing and a second surface opposite thefirst surface for facing a hot gas path, the critical process locationbeing located between the leading edge and the trailing edge when thebody is attached to the casing; and at least two cooling passagesdefined in the body related to one of the side edges, a first of thecooling passages having an inlet and extending to an outlet, one of theinlet or the outlet being adjacent the critical process location, asecond of the cooling passages having an inlet and extending to anoutlet, one of the inlet or the outlet being adjacent the criticalprocess location, the first and second cooling passages being configuredlarge enough to cool the one side edge to a desired level duringoperation of the gas turbine.
 2. The shroud segment of claim 1, whereinthe first cooling passage has a first portion along the leading edge anda second portion along the one side edge.
 3. The shroud segment of claim2, wherein the second cooling passage has a first portion along the oneside edge and a second portion along the trailing edge.
 4. The shroudsegment of claim 1, further including at least two additional coolingpassages along the other of the side edges, the two additional coolingpassages being substantially symmetrical to the at least two coolingpassages with reference to a central plane of the body extending betweenthe leading edge and the trailing edge.
 5. The shroud segment of claim1, wherein the first cooling passage has a second outlet adjacent thecritical process location along the other side edge.
 6. The shroudsegment of claim 5, wherein the first cooling passage includes a firstportion along the leading edge and a second portion along the one sideedge, a third portion along the leading edge, and a fourth portion alongthe other side edge.
 7. The shroud segment of claim 1, wherein thesecond cooling passage has a second inlet adjacent the critical processlocation along the other side edge.
 8. The shroud segment of claim 1,wherein the second cooling passage includes a first portion along theone side edge and a second portion along the trailing edge, a thirdportion along the other side edge, and a fourth portion along thetrailing edge.
 9. The shroud segment of claim 1, wherein the secondcooling passage includes multiple outlets.
 10. The shroud segment ofclaim 1, wherein the body and first and second cooling passages areconfigured of a cast metal.
 11. A gas turbine comprising: a compressorsection; a combustion section downstream from the compressor section;and a turbine section downstream from the combustion section, whereinthe turbine section includes a casing defining a localized criticalprocess location and a plurality of shroud segments circumferentiallyattached to the casing, each shroud segment including: a body configuredfor attachment to the casing, at least one of the bodies having aleading edge, a trailing edge, and two side edges, the body having afirst surface facing the casing and a second surface opposite the firstsurface facing a hot gas path, the critical process location beinglocated between the leading edge and the trailing edge when the body isattached to the casing; and at least two cooling passages defined in thebody related to one of the side edges, a first of the cooling passageshave an inlet and extending to an outlet, one of the inlet or the outletbeing adjacent the critical process location, a second of the coolingpassages having an inlet and extending to an outlet, one of the inlet orthe outlet being adjacent the critical process location, the first andsecond cooling passages being configured large enough to cool the oneside edge to a desired level during operation of the gas turbine. 12.The gas turbine of claim 11, wherein the first cooling passage has afirst portion along the leading edge and a second portion along the oneside edge.
 13. The gas turbine of claim 12, wherein the second coolingpassage has a first portion along the one side edge and a second portionalong the trailing edge.
 14. The gas turbine of claim 11, furtherincluding at least two additional cooling passages along the other ofthe side edges, the two additional cooling passages being substantiallysymmetrical to the at least two cooling passages with reference to acentral plane of the body extending between the leading edge and thetrailing edge.
 15. The gas turbine of claim 11, wherein the firstcooling passage has a second outlet adjacent the critical processlocation along the other side edge.
 16. The gas turbine of claim 15,wherein the first cooling passage includes a first portion along theleading edge and a second portion along the one side edge, a thirdportion along the leading edge, and a fourth portion along the otherside edge.
 17. The gas turbine of claim 11, wherein the second coolingpassage has a second inlet adjacent the critical process location alongthe other side edge.
 18. The gas turbine of claim 11, wherein the secondcooling passage includes a first portion along the one side edge and asecond portion along the trailing edge, a third portion along the otherside edge, and a fourth portion along the trailing edge.
 19. The gasturbine of claim 11, wherein the second cooling passage includesmultiple outlets.
 20. The gas turbine of claim 11, wherein the body andfirst and second cooling passages are configured of a cast metal.